Vapor sterilization using inorganic hydrogen peroxide complexes

ABSTRACT

An apparatus and process for hydrogen peroxide vapor sterilization of medical instruments and similar devices make use of hydrogen peroxide vapor released from an inorganic hydrogen peroxide complex. The peroxide vapor can be released at room temperature and atmospheric pressure; however, the pressure used can be less than 50 torr and the temperature greater than 86° C. to facilitate the release of hydrogen peroxide vapor. The heating rate can be greater than 5° C. Optionally, a plasma can be used in conjunction with the vapor.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/369,786, filed Jan. 6, 1995, which is a continuation-in-partof Ser. No. 08/234,738, filed Apr. 28, 1994 (now abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus and process for using hydrogenperoxide vapor to sterilize articles such as medical instruments, andmore particularly to the use of an inorganic hydrogen peroxide complexfor such a process.

2. Description of the Related Art

Medical instruments have traditionally been sterilized using eitherheat, such as is provided by steam, or a chemical, such as formaldehydeor ethylene oxide in the gas or vapor state. Each of these methods hasdrawbacks. Many medical devices, such as fiber optic devils, endoscopes,power tools, etc. are sensitive to heat, moisture, or both. Formaldehydeand ethylene oxide are both toxic gases that pose a potential hazard tohealthcare workers. Problems with ethylene oxide are particularlysevere, because its use requires long aeration times to remove the gasfrom articles that have been sterilized. This makes the sterilizationcycle time undesirably long. In addition, both formaldehyde and ethyleneoxide require the presence of a substantial amount of moisture in thesystem. Thus, devices to be sterilized must be humidified before thechemical is introduced or the chemical and moisture must be introducedsimultaneously. Moisture plays a role in sterilization with a variety ofother chemicals in the gas or vapor state, in addition to ethylene oxideand formaldehyde, as Table 1.

                  TABLE 1                                                         ______________________________________                                                    Relative Humidity Requirements                                                                  Literature                                      Chemical    for Optimal Efficacy                                                                            Reference                                       ______________________________________                                        Ethylene oxide                                                                            25-50%            1                                               Propylene oxide                                                                           25-50%            1                                               Ozone       75-90%            2                                               Formaldehyde                                                                              >75%              1                                               Glutaraldehyde                                                                            80-90%            3                                               Chlorine dioxide                                                                          60-80%            4                                               Methyl bromide                                                                            40-70%            1                                               β-Propiolactone                                                                      >75%              1                                               Peracetic acid                                                                            40-80%            5                                               ______________________________________                                         1. Bruch, C. W. Gaseous Sterilization, Ann. Rev. Microbiology 15:245-262      (1961).                                                                       2. Janssen, D. W. and Schneider, P. M. Overview of Ethylene Oxide             Alternative Sterilization Technologies, Zentralsterilisation 1:16-32          (1993).                                                                       3. Bovallius, A. and Anas, P. SurfaceDecontaminating Action of                Glutaraldehyde in the GasAerosol Phase. Applied and Environmental             Microbiology, 129-134 (Aug. 1977).                                            4. Knapp, J. E. et al. Chlorine Dioxide As a Gaseous Sterilant, Medical       Device & Diagnostic Industry, 48-51 (Sept. 1986).                             5. Portner, D. M. and Hoffman, R. K. Sporicidal Effect of Peracetic Acid      Vapor, Applied Microbiology 16:1782-1785 (1968).                         

Sterilization using hydrogen peroxide vapor has been shown to have someadvantages over other chemical sterilization processes (see, e.g., U.S.Pat. Nos. 4,169,123 and 4,169,124), and the combination of hydrogenperoxide with a plasma provides additional advantages, as disclosed inU.S. Pat. No. 4,643,876. In these disclosures the hydrogen peroxidevapor is generated from an aqueous solution of hydrogen peroxide, whichensures that there is moisture present in the system. These disclosures,together with those summarized in Table 1, teach that moisture isrequired for hydrogen peroxide in the vapor phase to be effective or toexhibit its maximum sporicidal activity. However, the use of aqueoussolutions of hydrogen peroxide to generate hydrogen peroxide vapor forsterilization may cause problems. At higher pressures, such asatmospheric pressure, excess water in the system can cause condensation.Thus, one must reduce the relative humidity in a sterilization enclosurebefore introducing the aqueous hydrogen peroxide vapor.

The sterilization of articles containing diffusion-restricted areas,such as long narrow lumens, presents a special challenge for hydrogenperoxide vapor that has been generated from an aqueous solution ofhydrogen peroxide, because:

1. Water has a higher vapor pressure than hydrogen peroxide and willvaporize faster than hydrogen peroxide from an aqueous solution.

2. Water has a lower molecular weight than hydrogen peroxide and willdiffuse faster than hydrogen peroxide in the vapor state.

Because of this, when an aqueous solution of hydrogen peroxide isvaporized, the water reaches the items to be sterilized first and inhigher concentration. The water vapor therefore becomes a barrier to thepenetration of hydrogen peroxide vapor into diffusion restricted areas,such as small crevices and long narrow lumens. One cannot solve theproblem by removing water from the aqueous solution and using moreconcentrated hydrogen peroxide, since concentrated solutions of hydrogenperoxide, i.e., greater than 65% by weight, can be hazardous, due to theoxidizing nature of the solution.

U.S. Pat. Nos. 4,642,165 and 4,744,951 attempt to solve this problem.The former discloses metering small increments of a hydrogen peroxidesolution onto a heated surface to ensure that each increment isvaporized before the next increment is added. Although this helps toeliminate the difference in the vapor pressure and volatility betweenhydrogen peroxide and water, it does not address the fact that waterdiffuses faster than hydrogen peroxide in the vapor state.

The latter patent describes a process for concentrating hydrogenperoxide from a relatively dilute solution of hydrogen peroxide andwater and supplying the concentrated hydrogen peroxide in vapor form toa sterilization chamber. The process involves vaporizing a major portionof the water from the solution and removing the water vapor producedbefore injecting the concentrated hydrogen peroxide vapor into thesterilization chamber. The preferred range for the concentrated hydrogenperoxide solution is 50% to 80% by weight. This process has thedisadvantage of working with solutions that are in the hazardous range;i.e., greater than 65% hydrogen peroxide, and also does not remove allof the water from the vapor state. Since water is still present in thesolution, it will vaporize first, diffuse faster, and reach the items tobe sterilized first. This effect will be especially pronounced in longnarrow lumens.

U.S. Pat. No. 4,943,414 discloses a process in which a vessel containinga small amount of a vaporizable liquid sterilant solution is attached toa lumen, and the sterilant vaporizes and flows directly into the lumenof the article as the pressure is reduced during the sterilizationcycle. This system has the advantage that the water and hydrogenperoxide vapor are pulled through the lumen by the pressure differentialthat exists, increasing the sterilization rate for lumens, but it hasthe disadvantage that the vessel needs to be attached to each lumen tobe sterilized. In addition, water is vaporized faster and precedes thehydrogen peroxide vapor into the lumen.

U.S. Pat. No. 5,008,106 discloses that a substantially anhydrous complexof PVP and H₂ O₂ is useful for reducing the microbial content ofsurfaces. The complex, in the form of a fine white powder, is used toform antimicrobial solutions, gels, ointments, etc. It can also beapplied to gauze, cotton swabs, sponges and the like. The H₂ O₂ isreleased upon contact with water present on the surfaces containing themicrobes. Thus, this method too requires the presence of moisture toeffect sterilization.

Certain inorganic hydrogen peroxide complexes have been reportedincluding examples within the following classes: alkali metal andammonium carbonates, alkali metal oxalates, alkali metal phosphates,alkali metal pyrophosphates, fluorides and hydroxides. U.S.S.R. patentdocument No. SU 1681860 (Nikolskaya et al.) discloses that surfaces canbe decontaminated, although not necessarily sterilized, using ammoniumfluoride peroxohydrate (NH₄ F.H₂ O₂). However, this inorganic peroxidecomplex provides decontamination only within the very narrow temperaturerange of 70°-86° C. Even within this range, decontamination times werequite long, requiring at least two hours. Additionally, it is known thatammonium fluoride decomposes to ammonia and hydrofluoric acid attemperatures above 40° C. Due to its toxicity and reactivity,hydrofluoric acid is undesirable in most sterilization systems.Moreover, Nikolskaya et al. disclose that despite the release of 90% ofits hydrogen peroxide at 60° C., NH₄ F.H₂ O₂ is ineffective atdecontamination of surfaces at this temperature. Thus, it appears that afactor other than hydrogen peroxide is responsible for thedecontamination noted.

Hydrogen peroxide is capable of forming complexes with both organic andinorganic compounds. The binding in these complexes is attributed tohydrogen bonding between electron rich functional groups in thecomplexing compound and the peroxide hydrogen. The complexes have beenused in commercial and industrial applications such as bleaching agents,disinfectants, sterilizing agents, oxidizing reagents in organicsynthesis, and catalysts for free-radical-induced polymerizationreactions.

Generally, these types of compounds have been prepared by thecrystallization of the complex from an aqueous solution. For example,urea hydrogen peroxide complex was prepared by Lu et al. (J. Am. Chem.Soc.63(1):1507-1513 (1941)) in the liquid phase by adding a solution ofurea to a solution of hydrogen peroxide and allowing the complex tocrystallize under the proper conditions. U.S. Pat. No. 2,986,448describes the preparation of sodium carbonate hydrogen peroxide complexby treating a saturated aqueous solution of Na₂ CO₃ with a solution of50 to 90% H₂ O₂ in a closed cyclic system at 0° to 5° C. for 4 to 12hours. More recently, U.S. Pat. No. 3,870,783 discloses the preparationof sodium carbonate hydrogen peroxide complex by reacting aqueoussolutions of hydrogen peroxide and sodium carbonate in a batch orcontinuous crystallizer. The crystals are separated by filtration orcentrifugation and the liquors used to produce more sodium carbonatesolution. Titova et al. (Zhurnal Neorg. Khim., 30:2222-2227, 1985)describe the synthesis of potassium carbonate peroxyhydrate (K₂ CO₃. 3H₂O₂) by reaction of solid potassium carbonate with an aqueous solution ofhydrogen peroxide at low temperature followed by crystallization of thecomplex from ethanol. These methods work well for peroxide complexesthat form stable, crystalline free-flowing products from aqueoussolution.

U.S. Pat. Nos. 3,376,110 and 3,480,557 disclose the preparation of acomplex of hydrogen peroxide with a polymeric N-vinylheterocycliccompound (PVP) from aqueous solution. The resultant complexes containedvariable amounts of hydrogen peroxide and substantial amounts of water.U.S. Pat. No. 5,008,093 teaches that free-flowing, stable, substantiallyanhydrous complexes of PVP and H₂ O₂ could be obtained by reacting asuspension of PVP and a solution of H₂ O₂ in an anhydrous organicsolvent like ethyl acetate. More recently, U.S. Pat. No. 5,077,047describes a commercial process for producing the PVP-hydrogen peroxideproduct by adding finely divided droplets of a 30% to 80% by weightaqueous solution of hydrogen peroxide to a fluidized bed of PVPmaintained at a temperature of ambient to 60° C. The resultant productwas found to be a stable, substantially anhydrous, free flowing powderwith a hydrogen peroxide concentration of 15 to 24%.

U.S. Pat. No. 5,030,380 describes the preparation of a solid polymericelectrolytic complex with hydrogen peroxide by first forming a complexin aqueous solution and then drying the reaction product under vacuum orby spray drying at a low enough temperature to avoid thermal degradationof the product.

All of these previous methods of preparing hydrogen peroxide complexesuse solutions of hydrogen peroxide. Either the complex is formed in asolution containing hydrogen peroxide or droplets of a hydrogen peroxidesolution are sprayed onto a fluidized bed of the reactant material.

Vapor phase and gas phase reactions are well known synthesis methods.For example, U.S. Pat. No. 2,812,244 discloses a solid-gas process fordehydrogenation, thermal cracking, and demethanation. Fujimoto et al.(J. Catalysis, 133:370-382 (1992)) described a vapor-phase carboxylationof methanol. Zellers et al. (Anal. Chem., 62:1222-1227 (1990)) discussedthe reaction of styrene vapor with a square-plannar organoplatinumcomplex. These prior art vapor- and gas-phase reactions, however, werenot used to form hydrogen peroxide complexes.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to an apparatus for hydrogenperoxide sterilization of an article. This apparatus includes acontainer for holding the article to be sterilized at a pressure of lessthan 50 torr. Preferably, the pressure is less than 20 torr, and morepreferably less than 10 torr. The apparatus also includes a source ofhydrogen peroxide vapor in fluid communication with the container. Thesource includes an inorganic hydrogen peroxide complex at a temperaturegreater than 86° C., and is configured so that the peroxide vapor cancontact the article to effect sterilization. The source can be locatedwithin the container, or alternatively, the apparatus can include anenclosure disposed outside of the container in which the complex islocated, and an inlet providing fluid communication betweeen thecontainer and the enclosure, such that vapor released from the complextravels along the inlet and into the container to effect sterilization.The inorganic hydrogen peroxide complex can be a complex of sodiumcarbonate, potassium pyrophosphate or potassium oxalate. Preferably, theapparatus, also includes a heater located within the container, wherebythe complex is placed on the heater and heated to facilitate the releaseof the vapor from the complex. Such a heater can be heated prior tocontacting with the complex. The apparatus can also include a vacuumpump in fluid communication with the container for evacuating thecontainer. In some embodiments, the apparatus includes an electrodeadapated to generate a plasma around the article. Such an electrode canbe inside the container, or can be spaced apart from the container andadapated to flow plasma generated thereby towards and around thearticle. In a preferred embodiment, the complex is in a solid phase.

Another aspect of the present invention relates to a method for hydrogenperoxide vapor sterilization of an article. This method includes placingthe article into a container, and contacting the article with a hydrogenperoxide vapor released from an inorganic hydrogen peroxide complex byheating the complex at a rate of at least 5° C./minute to contact andsterilize the article. Preferably, the heating rate is at least 10°C./minute, more preferably, at least 50° C./minute, and still morepreferably at least 1000° C./minute. The complex preferably has lessthan 10% water. The complex can be heated, preferably to a temperaturegreater than 86° C. to facilitate the release of the vapor from thecomplex. The container can be evacuated before introducing the vaporinto the container at a pressure of less than 50 torr, more preferablyless than 20 torr, and still more preferably less than 10 torr.Optionally, a plasma can be generated around the article afterintroducing the vapor into the container. The plasma can be generatedeither inside or outside of the container. The present invention alsoincludes a method for hydrogen peroxide vapor sterilization of anarticle in which the inorganic hydrogen peroxide complex used is onewhich does not decompose to release a hydrohalic acid.

Yet another aspect of the present invention relates to a method forhydrogen peroxide sterilization of an article using a self-sterilizingenclosure. In this method, the article is placed in a enclosurecontaining an inorganic hydrogen peroxide complex, the enclosure issealed, and the enclosure allowed to stand at a temperature below 70° C.for a time sufficient to release hydrogen peroxide vapor from thecomplex and effect sterilization of the article. Although not necessary,the enclosure can be allowed to stand at a pressure less thanatmospheric pressure or at a temperature above room temperature (23°C.).Thus, the enclosure can be allowed to stand at a temperature below about40° C. Any of a variety of enclosures can be used, e.g. a pouch, acontainer, a chamber or a room. Preferably, the hydrogen peroxidecomplex is in the form of a powder or tablet. The sealing step caninclude sealing the enclosure with a gas permeable material, such asTYVEK™, CSR wrap, or paper.

The present invention also relates to a sealed enclosure containing asterile product and an inorganic hydrogen peroxide complex capable ofreleasing hydrogen peroxide vapor.

Included within the present invention is also a potassium pyrophosphatehydrogen peroxide complex.

A further aspect of the invention relates to a method for hydrogenperoxide sterilization of an article having an exterior and a narrowlumen therein. This method involves connecting a vessel containing aninorganic peroxide complex to the lumen of the article, placing thearticle within a container, whereby the vessel remains connected to thelumen, reducing the pressure within the container, and contacting thelumen of the article with hydrogen peroxide vapor released from theinorganic peroxide complex at a temperature less than 70° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a vapor sterilization apparatus of the presentinvention.

FIG. 2 is a schematic of a vapor sterilization apparatus of the presentinvention which includes an electrode which is optionally used togenerate plasma.

FIG. 3A is a schematic of a device which can be used for heatingperoxide complexes.

FIG. 3B is a schematic of a preferred container for holding the peroxidesource for sterilization according to the present invention.

FIG. 4 is a graph depicting the release of hydrogen peroxide vapor froma vacuum unstable non-aqueous hydrogen peroxide complex.

FIG. 5 is a schematic of a pressure control system of a differentialscanning calorimeter (DSC) used to determine hydrogen peroxide releaseor decomposition properties of inorganic peroxide complexes according tothe present invention.

FIG. 6 is a graph showing the effect of pressure on hydrogen peroxiderelease from potassium oxalate peroxide complex.

FIG. 7A is a schematic view of a bellows for injecting peroxide vaporinto a chamber in accordance with the present invention before injectionof the peroxide vapor.

FIG. 7B is a schematic view of the bellows of FIG. 7A showing a heatedplate in contact with a peroxide complex during injection.

DETAILED DESCRIPTION OF THE INVENTION

Hydrogen peroxide sterilizers that have been used in the past invariablyused an aqueous solution of hydrogen peroxide as their source ofsterilant. These sterilizers have disadvantages caused by the presenceof water in the system. At higher pressure, such as atmosphericpressure, the excess water in the system can cause condensation. Thisrequires that an extra step be performed to reduce the relative humidityof the atmosphere in an enclosure to be sterilized to an acceptablelevel before the aqueous hydrogen peroxide vapor is introduced. Thesesterilizers also have drawbacks caused by the facts that water, having ahigher vapor pressure, vaporizes more quickly than hydrogen peroxidefrom an aqueous solution; and water, having a lower molecular weight,diffuses faster than hydrogen peroxide. When a medical device or thelike is enclosed in a sterilizer, the initial sterilant that reaches thedevice from the hydrogen peroxide source is diluted in comparison to theconcentration of the source. The dilute sterilant can be a barrier tosterilant that arrives later, particularly if the device beingsterilized is an article, such as an endoscope, that has narrow lumens.Using a concentrated solution of hydrogen peroxide as the source in anattempt to overcome these drawbacks is unsatisfactory, because suchsolutions are hazardous.

In the present invention, the shortcomings of hydrogen peroxidesterilizers of the prior art are overcome by using a substantiallynon-aqueous (i.e., substantially anhydrous) source of hydrogen peroxidewhich releases a substantially non-aqueous hydrogen peroxide vapor. In apreferred embodiment, the substantially non-aqueous hydrogen peroxidevapor is produced directly from a substantially nonaqueous hydrogenperoxide complex. However, the substantially non-aqueous hydrogenperoxide vapor can also be generated from an aqueous complex which isprocessed during vaporization to remove water, such as under vacuum.Thus, where an aqueous hydrogen peroxide complex is used, the aqueouscomplex can be converted to a substantially non-aqueous hydrogenperoxide complex while carrying out the process of the presentinvention. Preferably, the substantially non-aqueous hydrogen peroxidecomplexes contain less than about 20% water, more preferably no morethan about 10% water, still more preferably no more than about 5% water,and most preferably no more than about 2% water.

As is apparent from the preferred percentages of water in thesubstantially non-aqueous hydrogen peroxide complexes used in thepresent invention, as provided above, the most preferred hydrogenperoxide complex and the peroxide vapor generated therefrom aresubstantially water-free. Nevertheless, as is also apparent from thesefigures, some water can be present in the system. Some of this water mayderive from the decomposition of hydrogen peroxide to form water andoxygen as byproducts and some hydrogen binding of this water to thecomplex can occur.

The effect of water was measured in a series of tests, with asterilization chamber maintained at various relative humidities. Testconditions were those described in Example 1, below, with sporessupported on stainless steel (SS) blades in 3 mm×50 cm stainless steellumens. As shown in Table 2, under the test conditions, 5% relativehumidity has no effect on efficacy but 10% relative humidity decreasesthe sterilization rate. This example shows that small amounts ofmoisture can be allowed in the system with the hydrogen peroxidegenerated from the non-aqueous peroxide complex and the presence ofwater in the system can be overcome by increasing the exposure time.

                  TABLE 2                                                         ______________________________________                                        Effects of Relative Humidity on Efficacy                                      SS Blades in 3 mm × 50 cm SS Lumens                                              Sterility Results (Positive/Samples)                                 Diffusion Time                                                                           1% RH       5% RH    10% RH                                        ______________________________________                                        5          0/3         0/3      3/3                                           10         0/3         0/3      2/3                                           15         0/3         0/3      0/3                                           30         0/3         0/3      0/3                                           ______________________________________                                    

A primary criterion for the composition of the hydrogen peroxide sourceis the relationship between its stability and hydrogen peroxideevaporation rate as a function of temperature and pressure. Depending onthe parameters of the sterilization process--e.g. pressure, temperature,etc.--a higher or lower peroxide evaporation rate may be preferred, andheating the peroxide source may or may not be required. The need forheating of the peroxide complex depends on the vapor pressure of thecomplex. Some peroxide complexes have a sufficiently high vapor pressurethat a significant amount of hydrogen peroxide vapor can be releasedwithout heating the complex. In general, heating the complex increasesthe vapor pressure of hydrogen peroxide and accelerates the release ofperoxide from the complex.

To provide a desirably high evaporation rate, the source shouldpreferably have a large surface area. Thus the source may be a finepowder or a coating on a material that has a large surface area. Ofcourse, safety, availability, and cost of the material are alsoimportant criteria. The release of hydrogen peroxide from hydrogenperoxide complexes with urea, polyvinylpyrrolidone, nylon-6, glycineanhydride, and 1,3 dimethyl urea were evaluated. The complexes ofhydrogen peroxide with urea, polyvinylpyrrolidone, nylon-6, and glycineanhydride are solids. The 1,3 dimethyl urea peroxide complex is aliquid. The glycine anhydride hydrogen peroxide complex is a less stablecomplex under reduced pressure than the other complexes evaluated, andunder vacuum conditions, most of the hydrogen peroxide can be releasedfrom the complex without the need for additional heating.

Urea hydrogen peroxide complex is available in tablet form from FlukaChemical Corp., Ronkonkoma, N.Y. and in powder form from AldrichChemical Co., Milwaukee, Wis. This complex is also known as ureaperoxide, hydrogen peroxide urea complex, peroxide urea, peroxide ureaadduct, urea peroxide adduct, percarbamide, carbamide perhydrate, andcarbamide peroxide. As used herein, the term "urea peroxide" encompassesall of the foregoing terms.

The polyvinylpyrrolidone-hydrogen peroxide complex (PVP-H₂ O₂) can beprepared by the method disclosed in International Application Pub. No.WO 92/17158. Alternatively, the complexes with PVP, with nylon-6, with1,3 dimethylurea and with glycine anhydride, as well as with otherorganic and inorganic compounds can be prepared by the method disclosedin detail below.

Achieving suitable evaporation rates of anhydrous peroxide vapor fromthe source may be facilitated by elevated temperatures and/or reducedpressure. Thus, a heater for the peroxide source and/or a vacuum pump toevacuate the sterilization chamber are preferably a part of thesterilizer. Preferably, the source is covered with a layer of gaspermeable material, such as TYVEK™ nonwoven polyethylene fabric,nonwoven polypropylene such as SPUNGUARD™, or similar material, whichpermits the peroxide vapor to pass but not the peroxide complexingmaterial. Perforated aluminum or other suitable perforated materialcould also be used as a cover.

FIG. 3A shows a device 80 that can be used to measure release ofhydrogen peroxide from hydrogen peroxide complexes under varioustemperature conditions. In this device, an aluminum pan 90 is coveredwith a gas permeable layer 92, such as a layer of medical grade TYVEK™.The pan 90 is placed on top of a heating part 94 which is placed in apyrex pan 96. A thermocouple thermometer 98 is placed on the outside ofthe pan 90 approximately 1 cm from the bottom thereof.

A preferred container 99 for holding the peroxide source is illustratedin FIG. 3B. The container 99 comprises a metal plate 100, e.g. analuminum plate, with an optional attached heater used to heat the solidperoxide complex. A temperature monitor 101, such as a thermometer, canbe placed on the plate 100 to monitor the temperature. The peroxidecomplex is placed directly on the plate 100. Alternatively, in order toprovide even heating of all the peroxide complex, the peroxide complexcan be placed between one or more aluminum screens 102, 104 placed ontop of the plate 100. The aluminum screens 102, 104 provide greatersurface area and even heating of the complex when larger amounts ofperoxide complex are being used. The peroxide complex, or the screen orscreens 102, 104, are then covered with a gas permeable layer 106, suchas a layer of medical grade TYVEK™ or SPUNGUARD™, so that the hydrogenperoxide released from the complex passes through the covering 106before diffusing into the rest of the chamber. A perforated aluminumplate 108 is optionally placed on top of the TYVEK™ or SPUNGUARD™ layer106 to provide pressure to keep the complex in contact with the heatedplate 100 and to ensure even heating of the peroxide complex.

The device just described provides even heating of the complex, whichresults in an increased amount of hydrogen peroxide vapor being releasedfrom the peroxide complex.

FIG. 1 depicts a schematic of a hydrogen peroxide vapor sterilizationapparatus of the present invention. Chamber 10 holds an article 12 whichis to be sterilized and which, for convenience, is placed on shelf 14.Door 16 provides access to the interior of chamber 10. A non-aqueoussource of hydrogen peroxide 18 is depicted on optional heater 20, whichis controlled by temperature controller 22. The peroxide concentrationcan be monitored by optional monitor 24. If desired, chamber 10 can beevacuated using pump 26; however, sterilization can also be accomplishedat atmospheric pressure.

The container that holds the articles to be sterilized can be aconventional sterilization chamber, which is evacuated, or it can be acontainer (or a room) at atmospheric pressure.

The time required to sterilize the articles depends on the nature,number and packaging of the articles and their placement in the chamber.Alternatively, it may be the chamber itself (or an entire room) that isbeing sterilized. In any case, optimum sterilization times can bedetermined empirically.

The use of pressure pulsing to enhance the penetration and antimicrobialactivity of sterilant gases, which is well known in the sterilizationart, can also be applied to the non-aqueous hydrogen peroxide process.As described in additional detail hereinbelow, plasma can also be usedto further enhance activity.

At the conclusion of the sterilization process excess hydrogen peroxidecan be removed from devices that have an affinity for peroxide byexchanging the air in contact with the devices. This can be accomplishedby flowing warm air over the devices for an extended time or byevacuating the chamber.

Articles that have previously been sterilized by exposure to hydrogenperoxide vapor may also be exposed to the plasma to remove residualhydrogen peroxide that may remain on the articles. Since the hydrogenperoxide is decomposed into non-toxic products during the plasmatreatment, the sterilized articles may be used without the need for anyadditional steps.

It may be desirable to isolate the peroxide source from the sterilizerafter the peroxide vapor is released to avoid reabsorption of the vaporor, when a plasma is used, to avoid exposing the source to the plasma.Isolation is also advantageous when the complex used is not stable undervacuum. Isolation can be accomplished using valves or other isolatingdevices well known in the art.

FIG. 2 depicts a schematic of a hydrogen peroxide plasma sterilizationsystem of the present invention. Sterilization can be achieved with orwithout the use of plasma. The plasma can be used to enhance thesporicidal activity of the peroxide vapor, and/or to remove any residualhydrogen peroxide remaining on the sterilized articles.

Sterilization is carried out in chamber 30, which includes a door oropening 32 through which articles to be sterilized can be introduced.The chamber 30 includes an outlet 34 to a vacuum pump 36, through whichthe chamber can be evacuated. The outlet 34 contains a valve 38 toisolate the chamber from the vacuum pump 36. The chamber 30 alsoincludes an inlet 40 attached to an enclosure 42 that contains thehydrogen peroxide complex. Inlet 40 contains a valve 44 that allowsenclosure 42 to be isolated from the chamber. The sterilization systemalso contains an inlet 41 which connects the enclosure 42 and the vacuumpump 36, which contains a valve 43. This system allows the simultaneousevacuation of both enclosure 42 and chamber 30, or the independentevacuation of either enclosure 42 or chamber 30. Evacuation iscontrolled by the opening and closing of the valves 38, 44, and 43. Aswill be apparent to one having ordinary skill in the art, two pumps, onefor each chamber, could also be employed in this system.

The enclosure 42 contains an optional heater 49 attached to atemperature controller 46 to control the temperature of the hydrogenperoxide complex. The hydrogen peroxide complex concentration in thevapor state can be monitored by an optional peroxide monitor 48. Theinterior of the chamber contains a radio frequency (RF) electrode 50, towhich is attached a matching network 52 and an RF power supply 54. Aconvenient form for the electrode is a perforated cylinder, surroundingthe samples and open at both end. The general operation of the presentprocess is as follows:

1. The articles 56 to be sterilized are placed in the chamber 30.

2. The chamber 30 may be at atmospheric pressure or, alternatively, maybe evacuated to facilitate penetration of the hydrogen peroxide.Evacuation is accomplished by opening valve 38 and turning on vacuumpump 36. Alternatively, both the chamber 30 and the enclosure 42 may beevacuated by opening valves 38 and 44, and/or 43.

3. The valves 38 and 43 are closed to isolate the vacuum pump 36 fromthe chamber 30 and enclosure 42, and the valve 44 is opened. Hydrogenperoxide vapor is delivered into chamber 30 from the hydrogen peroxidesource, which may be heated to facilitate the release of the hydrogenperoxide vapor. Optionally, air or an inert gas may also be added.

4. The articles 56 to be sterilized are either treated with peroxidevapor until sterilized or pretreated with peroxide vapor in the chamber30 before plasma with sufficient power to sterilize is generated. Ifnecessary, chamber 30 may be evacuated at this time to facilitategeneration of the plasma. The duration of the pre-plasma holding perioddepends on the type of package used, the nature and number of items tobe sterilized, and the placement of the items in the chamber. Optimumtimes can be determined empirically.

5. The articles 56 are subjected to a plasma by applying power from theRF power supply 54 to the RF electrode 50. The RF energy used togenerate the plasma may be pulsed or continuous. The articles 56 remainin the plasma for a period to effect complete sterilization and/or toremove residual hydrogen peroxide. In certain embodiments, 5 to 30minutes of plasma is used. However, optimum times can be determinedempirically.

When used in the present specification and claims, the term "plasma" isintended to include any portion of the gas or vapor that containselectrons, ions, free radicals, dissociated and/or excited atoms ormolecules produced as a result of an applied electric field, includingany accompanying radiation that might be produced. The applied field maycover a broad frequency range; however, a radio frequency or microwavesare commonly used.

The non-aqueous hydrogen peroxide delivery system disclosed in thepresent invention can also be used with plasmas generated by the methoddisclosed in the previously mentioned U.S. Pat. No. 4,643,876.Alternatively, it may be used with plasmas described in U.S. Pat. No.5,115,166 or 5,087,418, in which the article to be sterilized is locatedin a chamber that is separated from the plasma source.

The device just described is particularly advantageous when usingperoxide complexes that are not stable under vacuum. There are at leasttwo possible methods that can be used to minimize the loss of hydrogenperoxide during the vacuum stage. First, the small chamber can beevacuated independently. Second, if a small enough chamber is used,there is no need to evacuate the small chamber at all.

One such unstable non-aqueous peroxide complex is glycineanhydride-peroxide. This compound releases hydrogen peroxide vapor whenplaced under vacuum. FIG. 4 is a graph illustrating the release ofhydrogen peroxide vapor from glycine anhydride-peroxide complex undervacuum. The procedure used to release the hydrogen peroxide from theglycine anhydride complex is as follows: (1) The main chamber 30 wasevacuated with valves 43 and 44 closed. (2) The chamber containing thehydrogen peroxide complex 42 was evacuated with valves 38 and 44 closedand valve 43 open. (3) Valve 43 was closed and valve 44 was opened andhydrogen peroxide vapor was allowed to diffuse into chamber 30.

As shown by the graph, hydrogen peroxide vapor is released from thecomplex as the pressure is reduced, even without additional heating. Asillustrated in FIG. 4, release of peroxide vapor is significantlyincreased by heating the complex to a higher temperature. Thus, evenunstable peroxide complexes are useful in the sterilization method ofthe present invention.

The present invention provides at least four advantages over earlierhydrogen peroxide sterilization systems:

1. The use of concentrated, potentially hazardous hydrogen peroxidesolutions is circumvented.

2. The need to reduce beforehand the relative humidity of areas to besterilized in order to prevent condensation is eliminated.

3. Water is substantially eliminated from the system, so that there islittle competition between water and hydrogen peroxide for diffusioninto long narrow lumens.

4. The need to attach a special vessel to deliver sterilant gases intolong narrow lumens can often be eliminated.

That sterilization can be effected using hydrogen peroxide vapor in thesubstantial absence of moisture is one of the surprising discoveries ofthe present invention. The prior art teaches that the presence of wateris required to achieve sterilization in chemical gas or vapor statesterilization processes. Advantageously, the present inventionsubstantially eliminates water from the system, which results in faster,more efficient and effective sterilization.

The sterilization efficacy of various non-aqueous hydrogen peroxidecomplexes was determined as described below in Example 1-4.

EXAMPLE 1

Efficacy data was obtained with hydrogen peroxide vapor released fromsubstantially anhydrous urea peroxide complex using Bacillus subtilisvar. (niger) spores in metal and TEFLON™ plastic lumens as thebiological challenge.

A. Test Procedures

1. Equipment

Four grams of crushed hydrogen peroxide urea adduct tablet (FlukaChemical Corp, Ronkonkoma, N.Y.) were placed in an aluminum pan 90, asdescribed in FIG. 3A. The top of the pan 90 was covered with medicalgrade TYVEK™ 92 (a breathable spunbond polyethylene fabric) so that anyhydrogen peroxide released from the complex would need to pass throughthe TYVEK™ covering before diffusing into the rest of the chamber. Thealuminum pan 90 was placed on a heating part 94 in a pyrex dish 96located in the bottom of an aluminum sterilization chamber (see FIG. 1).The sterilization chamber, which had an approximate volume of 173liters, also contained:

A hydrogen peroxide monitor for measuring hydrogen peroxideconcentration in the vapor phase.

A temperature controller for controlling the temperature of the heatingpad.

An injection port through which liquid hydrogen peroxide could beinjected into the chamber.

A metal shelf on which a plastic tray containing lumen devices wereplaced for testing.

Electrical resistance heaters on the exterior of the chamber walls,which maintained the chamber temperature at 45° C. during the efficacytestings.

2. Biological Challenge and Test

To evaluate the efficacy of the non-aqueous peroxide delivery system, abiological challenge consisting of 1.04×10⁶ B. subtilis var. (niger)spores on a stainless steel scalpel blade was placed equally distantfrom each end of the stainless steel lumens of dimensions 3 mm ID×40 cmlength, 3 mm ID×50 cm length, and 1 mm ID×50 cm length. These ID's andlengths are typical for metal lumens used in medical devices. Thecompartment in the middle of each lumen that contained the biologicaltest piece had the dimensions 13 mm ID×7.6 cm length. In the biologicaltesting with metal lumens, a total of 9 lumens were evaluated per test.These included 3 lumens from each of the 3 different sets of ID's andlengths available.

Similar tests were conducted with a biological challenge consisting of4.1×10⁵ B. subtilis var. (niger) spores on a paper strip (6 mm×4 mmWhatman #1 chromatography paper) located equally distant from the endsof TEFLON™ lumens of dimensions 1 mm ID×1 meter length, 1 mm ID×2 meterlength, 1 mm ID×3 meter length, and 1 mm ID×4 meter length. The centercompartment of these lumens that contained the biological test piece hadthe dimensions 15 mm ID×7.6 cm length. In the biological testing withTEFLON™ lumens, a total of 12 lumens were evaluated per test, 3 lumensfrom each of the 4 different lengths available.

The lumens containing the biological test samples were placed in aplastic tray that was then placed on the shelf in the sterilizationchamber. The chamber door was then closed and the chamber evacuated to0.2 Torr pressure with a vacuum pump. The aluminum pan containing thehydrogen peroxide urea adduct was then heated to 80° to 81° C. for aperiod of 5 minutes, as measured by a thermocouple thermometer placed onthe side wall of the aluminum pan approximately 1 cm from the bottom ofthe pan. During this time the concentration of hydrogen peroxide in thechamber increased to 6 mg/L as measured by the peroxide monitor.

The biological test samples were exposed to the hydrogen peroxide vaporfor periods of 5, 10, 15, 20, and 25 minutes. After exposure to thehydrogen peroxide vapor, the biological test samples were asepticallytransferred into 15 mL of trypticase soy broth containing 277 units ofcatalase to neutralize any hydrogen peroxide residuals that may remainon the test samples. All samples were incubated for 7 days at 32° C. andobserved for growth.

Comparative studies were also conducted in which a 50% aqueous solutionof hydrogen peroxide was injected into the sterilization chamber andvaporized from a heated injector (a heated metal surface). The volume ofhydrogen peroxide solution injected produced a vapor phase concentrationof hydrogen peroxide of 6 mg/L. The test lumens and biological testsamples used in these tests were identical to those used in thenon-aqueous hydrogen peroxide tests. The handling of the biological testsamples after exposure to the hydrogen peroxide was also identical.

B. Test Results

The results of these tests with stainless steel and TEFLON™ lumens,which are presented in Tables 3 and 4, respectively, illustrate theadvantages of the non-aqueous peroxide delivery system with both metaland non-metal lumens. Total kill of the bacterial spores was achievedwithin 5 minutes with the non-aqueous peroxide delivery system for thesmallest ID and the longest lumens evaluated. At the same time, totalkill was not achieved even after 25 minutes of diffusion time with the50% hydrogen peroxide solution.

                  TABLE 3                                                         ______________________________________                                        Aqueous/Non-Aqueous Efficacy Comparison                                       SS Blades in SS Lumens                                                                        STERILITY RESULTS                                                             (POSITIVE/SAMPLES)                                            SOURCE OF   DIFFUSION 3 mm ×                                                                           3 mm ×                                                                         1 mm ×                            PEROXIDE    TIME (MIN)                                                                              40 cm    50 cm  50 cm                                   ______________________________________                                        50% SOLUTION                                                                              5         3/3      3/3    3/3                                                 10        0/3      2/3    3/3                                                 15        1/3      1/3    1/3                                                 20        0/3      0/3    1/3                                                 25        0/3      0/3    1/3                                     UREA PEROXIDE                                                                             5         0/3      0/3    0/3                                                 10        0/3      0/3    0/3                                                 15        0/3      0/3    0/3                                                 20        0/3      0/3    0/3                                                 25        0/3      0/3    0/3                                     ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Aqueous/Non-Aqueous Efficacy Comparison                                       6 mm × 4 mm Paper strip in TEFLON ™ Lumens                                          STERILITY RESULTS                                                             (POSITIVE/SAMPLES)                                             SOURCE OF  DIFFUSION 1 mm ×                                                                          1 mm ×                                                                        1 mm ×                                                                        1 mm ×                         PEROXIDE   TIME (MIN)                                                                              1 m     2 m   3 m   4 m                                  ______________________________________                                        50% SOLUTION                                                                             5         3/3     3/3   3/3   3/3                                             10        3/3     3/3   3/3   3/3                                             15        0/3     1/3   1/3   2/3                                             20        0/3     0/3   1/3   1/3                                             25        0/3     0/3   0/3   1/3                                  UREA PEROXIDE                                                                            5         0/3     0/3   0/3   0/3                                             10        0/3     0/3   0/3   0/3                                             15        0/3     0/3   0/3   0/3                                             20        0/3     0/3   0/3   0/3                                             25        0/3     0/3   0/3   0/3                                  ______________________________________                                    

The fact that rapid sterilization can be accomplished in the absence ofsubstantial amounts of water is surprising, in light of the fact thatmoisture has generally been present during chemical gas/vapor phasesterilization by various sterilants other than hydrogen peroxide. Sincevapor phase hydrogen peroxide sterilization systems have used aqueoussolutions of hydrogen peroxide, there has been moisture present in thosesystems as well.

To test the sterilization efficacy of various other peroxide complexes,the following experiments were performed.

EXAMPLES 2, 3 and 4

The apparatus of Example 1 was used to test the efficacy ofpolyvinylpyrrolidone-hydrogen peroxide complex (Example 2), nylon6-hydrogen peroxide complex (Example 3), and 1,3 dimethylurea hydrogenperoxide complex (Example 4). These compounds were synthesized accordingto the method disclosed below in Examples 12 and 13. Test parameterswere as follows:

    ______________________________________                                                       Example                                                                       2      3        4                                              ______________________________________                                        Chamber Temp.    45° C.                                                                          45° C.                                                                          45° C.                              Initial Pressure 0.2 Torr 1.0 Torr 1.0 Torr                                   Wt. % of peroxide                                                                              17%      10.5%    26.6%                                      Peroxide concentration                                                                         6 mg/L   6 mg/L   6 mg/L                                     Wt. of complex used                                                                            8 g      18 g     6 g                                        per cycle                                                                     Temp to release peroxide                                                                       110° C.                                                                         110° C.                                                                         80° C.                              ______________________________________                                    

In each case, spore supports were 6 mm×4 mm paper substrates in plasticlumens and stainless steel blades in stainless steel lumens. The resultsof this efficacy testing appear below in Table 5.

                  TABLE 5                                                         ______________________________________                                        Efficacy of Complexes with PVP,                                               nylon 6, and 1,3-dimethylurea                                                                     STERILITY RESULTS                                                             (POSITIVE/SAMPLES)                                        TYPE OF  SIZE OF    With 5 Minutes Exposure                                   LUMEN    LUMENS     Example 2 Example 3                                                                            Example 4                                ______________________________________                                        TEFLON ™                                                                            1 mm × 1 m                                                                         0/3       0/3    0/3                                               1 mm × 2 m                                                                         0/3       0/3    0/3                                               1 mm × 3 m                                                                         0/3       0/3    0/3                                               1 mm × 4 m                                                                         0/3       0/3    0/3                                      STAINLESS                                                                              3 mm × 40 cm                                                                       0/3       0/3    0/3                                      STEEL    3 mm × 50 cm                                                                       0/3       0/3    0/3                                               1 mm × 50 cm                                                                       0/3       0/3    0/3                                      ______________________________________                                    

The results appearing in Table 5 show that each of the tested hydrogenperoxide complexes generate peroxide vapor which provides efficientsterilization after only five minutes exposure.

The temperature required to release the hydrogen peroxide vapor from thesolid complex which is shown above is the temperature measured by athermocouple thermometer located on the outside of the aluminum panapproximately 1 cm from the bottom of the pan. Further testing using athermometer, such as a fluoroptic thermometer, placed on the insidebottom of the pan indicated that the temperature at the bottom of thepan was approximately 30°-35° C. higher, as described in Example 5below. Thus, in the previous example, the temperature at the bottom ofthe pan was approximately 110°-115° C. when the thermocouple thermometerread 80° C., and the temperature at the bottom of the pan wasapproximately 140°-145° C. when the thermocouple thermometer read 110°C.

EXAMPLE 5

To determine the temperature at the bottom of the aluminum pan used tocontain the solid peroxide complex, a fluoroptic thermometer was tapedto the inside bottom of the aluminum pan. An Omega™ thermocouplethermometer was placed on the outside of the aluminum pan approximately1 cm from the bottom of the pan. Three different readings of thethermometers were taken. Each time the pan was heated to the desiredtemperature indicated by the thermometer placed on the side of the pan,allowed to cool, and then re-heated to the desired temperature. Therecorded temperatures are listed below:

    ______________________________________                                        Temp. at     Temp. at bottom of pan (°C.)                              side of pan  1st    2nd        3rd  avg                                       ______________________________________                                         80° C.                                                                             110.9  110.6      110.6                                                                              110.7                                     100° C.                                                                             131.5  132.6      132.0                                                                              132.0                                     ______________________________________                                    

The results show that the temperature at the bottom of the aluminum panwas approximately 30°-35° C. higher than the temperature indicated bythe thermocouple thermometer located at the side of the pan.

Further testing was performed to compare the efficacy data obtainedusing an aqueous and non-aqueous source of peroxide in an open(non-lumen) system. The experiments are described in detail below.

EXAMPLE 6

The apparatus of Example 1 was used with a biological challenge thatconsisted of 6.8×10⁵ B. subtilis var (niger) spores on a 6 mm×4 mm stripof Whatman #1 chromatography paper packaged in a TYVEK™/MYLAR™ envelope.(TYVEK™ is a gas permeable fabric made of polyethylene. MYLAR™ is anon-gas permeable polyester material). Packaged biological challengestrips were placed in the front, middle and back of a polyphenyleneoxide tray that contained a flexible fiberoptic sigmoidoscope. The traywas placed in a polyphenylene oxide container that had one port in thetop and two ports in the bottom to allow for diffusion. The four-inchdiameter ports were covered with a breathable polypropylene packagingmaterial (SPUNGUARD™ Heavy Duty Sterilization Wrap, Kimberly-Clark,Dallas, Tex.) to maintain the sterility of the contents of the containerafter sterilization. The container was placed in the apparatus ofExample 1 and the pressure in the chamber was reduced to 0.2 Torr. Thealuminum pan containing 2 grams of hydrogen peroxide urea adduct (FlukaChemical Corp.) was then heated to 80° to 81° C., as measured by athermocouple thermometer placed on the outside of the aluminum panapproximately 1 cm from the bottom of the aluminum pan, for 5 minutes toprovide 3 mg/L of hydrogen peroxide vapor in the chamber. The biologicaltest samples were exposed to the hydrogen peroxide vapor for periods of5 and 10 minutes. After exposure the test samples were handled in thesame way as were those in Example 1.

Comparative studies were also conducted in which a 50% aqueous solutionof hydrogen peroxide was injected into the sterilization chamber andvaporized from a heated injector. The volume of hydrogen peroxidesolution injected produced a vapor phase concentration of 3 mg/L. Thetest configuration, the composition of the biological test samples, andthe handling of the biological test samples after exposure were allidentical to those used in the non-aqueous hydrogen peroxide tests. Theresults of these tests are presented in Table 6.

                  TABLE 6                                                         ______________________________________                                        Aqueous/Non-Aqueous Efficacy                                                  Comparison in Open System                                                     (Non-Lumen Test)                                                                            Diffusion                                                                              Sterility                                              Source of     Time     Results                                                Peroxide      (min)    (positive/samples)                                     ______________________________________                                        50% solution  5        3/3                                                                  10       3/3                                                    Urea Peroxide 5        1/3                                                                  10       0/3                                                    ______________________________________                                    

The results of these tests demonstrate the greater efficacy of thenon-aqueous when compared with the aqueous hydrogen peroxide process inan "open" system in which the biological sample was not placed in alumen. Again, it was surprisingly discovered that a non-aqueous systemprovided superior sterilization even when diffusion of hydrogen peroxideinto a long and narrow lumen is not required. This suggests that themode of action of hydrogen peroxide is not the same for systems with andwithout water.

Further testing was performed to determine the efficacy a non-aqueousperoxide vapor at normal, not reduced, pressure. This testing isdetailed below.

EXAMPLE 7

Efficacy tests were conducted with the hydrogen peroxide vapor releasedfrom the urea peroxide complex in an open system at atmosphericpressure. In this test the biological challenge of 1.04×10⁶ B. subtilisvar. (niger) spores on the stainless steel surgical blades were packagedin a TYVEK™/MYLAR™ envelope. Packaged biological challenge blades wereplaced on the front, middle, and back of a polyphenylene oxide tray. Thetray was placed in the apparatus of Example 1 and the chamber door wasclosed. The aluminum pan containing 4.0 gm of urea peroxide (FlukaChemical Corp.) was heated to 80° to 81° C., as measured by athermocouple thermometer placed on the side of the aluminum panapproximately 1 cm from the bottom of the pan, for the duration of thetest. The biological test samples were exposed to the hydrogen peroxidevapor for periods of 5, 10, 20 and 30 minutes. After exposure the testsamples were handled the same way as those in Example 1. The results ofthese tests are presented in Table 7 and demonstrate the efficacy of thenon-aqueous peroxide process in an open system at atmospheric pressure.

                  TABLE 7                                                         ______________________________________                                        Efficacy of non-aqueous peroxide process in open system                       at atmospheric pressure                                                                     Diffusion                                                                              Sterility                                              Source of     Time     Results                                                Peroxide      (minutes)                                                                              (positive/samples)                                     ______________________________________                                        Urea          5        3/3                                                    Peroxide      10       1/3                                                                  20       0/3                                                                  30       0/3                                                    ______________________________________                                    

Further tests were conducted to determine the approximate amount ofperoxide released from the hydrogen peroxide urea complex at varioustemperatures. This testing is described in Example 8.

EXAMPLE 8

Urea peroxide powder, obtained from crushing the commercially availabletablets (Fluka Chemical Corp.), was placed between two aluminum screensin an apparatus according to FIG. 3B having dimensions 12.7 cm ×12.7 cm.The aluminum plate was then heated and the temperature was monitoredusing a thermometer located near a corner of the aluminum plate. Table 8lists the approximate percent of peroxide released at varioustemperatures after heating for five minutes. The data show thatapproximately 100% of the peroxide is released from the complex at atemperature of 140° C. Lesser percentages of peroxide are released atlower temperatures.

                  TABLE 8                                                         ______________________________________                                        Release of non-aqueous peroxide at various temperatures                       Heating Temperature                                                                           % Peroxide Released                                           ______________________________________                                         80° C.  ˜25%                                                    100° C.  ˜65%                                                    120° C.  ˜80%                                                    130° C.  ˜90%                                                    140° C.  ˜100%                                                   ______________________________________                                    

Peroxide complexes having the ability to release hydrogen peroxide vaporat room temperature and atmospheric pressure, such as the urea peroxidecomplex, allows them to be effective for use in various sterilizationapplications. Not only can they be used in the sterilization apparatusof the present invention described above, the compounds of the presentinvention can also be used as part of self-sterilizing packagingmaterials, or applied onto supports such as gauze, sponge, cotton, andthe like. The compounds allow for sterilization of sealed packages atroom temperature or at elevated temperatures, and are particularlyuseful for the sterilization of packaged medical or surgical products.

Particular uses of the compounds of the present invention are describedin the examples which follow. The peroxide complex used in the followingexamples was urea peroxide in the form of a tablet (Fluka ChemicalCorp.) or in the form of a powder obtained by crushing the tablets.

EXAMPLE 9

A self-sterilizing pouch was assembled as follows: A surgical scalpelhaving 3.8×10⁵ B. subtilis var. niger spores on its surface was placedin a sterile petri dish. The dish was placed in a larger petri dish,together with 1 gm urea peroxide complex in either tablet or powderform. The larger petri dish was then inserted into a pouch formed ofTYVEK™/MYLAR™ (gas permeable, Table 9), MYLAR™/MYLAR™ (non-gaspermeable, Table 10) or Paper/MYLAR™ (gas permeable, Table 10). Thepouch was then sealed.

Each pouch was exposed to various temperatures for various time periods,as shown in Tables 9 and 10 below. The biological test samples wereevaluated for sterilization as described in Example 1. The results areincluded in Tables 9 and 10, with a "+" sign indicating bacterialgrowth.

                  TABLE 9                                                         ______________________________________                                        Self-Sterilizing Pouches                                                      With Breathable Barrier (TYVEK ™/MYLAR ™)                               Temperature                                                                            Peroxide Type                                                                             1 hr.   2 hr. 3 hr. 4 hr.                                ______________________________________                                        23° C.                                                                          powder      +       -     -     -                                             table       +       +     -     -                                    40° C.                                                                          powder      -       -     -     -                                             tablet      -       -     -     -                                    60° C.                                                                          powder      -       -     -     -                                             tablet      -       -     -     -                                    ______________________________________                                    

Table 10 lists the efficacy data for self-sterilizing pouches with(Paper/MYLAR™) and without (MYLAR™/MYLAR™) a breathable barrier. Thepouches were assembled as described above, however the peroxide vaporsource was urea peroxide in powder form only.

                  TABLE 10                                                        ______________________________________                                        Self-Sterilizing pouches With & Without Breathable Barrier                    Temperature Packaging Type 2 hr.  4 hr.                                       ______________________________________                                        23° C.                                                                             MYLAR/MYLAR    -      -                                                       Paper/MYLAR    +      -                                           40° C.                                                                             MYLAR/MYLAR    -      -                                                       Paper/MYLAR    -      -                                           60° C.                                                                             MYLAR/MYLAR    -      -                                                       Paper/MYLAR    -      -                                           ______________________________________                                    

Results from this testing show that the urea peroxide complex of thepresent invention included in a pouch with and without a breathablebarrier provides effective sterilization to an article inside the pouchin the absence of moisture at room temperature and atmospheric pressureafter only 2 to 3 hours. At higher temperatures, sterilization iseffected after only one hour.

To determine the efficacy of the sterilization system of the presentinvention in a closed container, the following experiment was performed.

EXAMPLE 10

A self-sterilizing container was assembled as follows: A stainless steelsupport having either 3.8×10⁵ B. subtilis var. niger spores on itssurface (Table 11) or having 9.2×10⁵ B. subtilis var. niger spores onits surface (Table 12), was placed inside a small polyethylene (PE) vialhaving 20 holes (3/16" in size) in its surface. The vial was placed in alarger PE vial, which was covered with either an air tight cap, or a gaspermeable layer of SPUNGUARD® (CSR Wrap). Also included in the largervial was a second PE vial, also having 20 holes (3/16" in size) in itssurface. This vial contained 1 gm urea peroxide in either powder ortablet form, and was sealed in either a SPUNGUARD™ (CSR wrap) or TYVEK™pouch.

Each container was exposed to various temperatures for various timeperiods, as shown in Tables 11 and 12 below. The biological test sampleswere evaluated for sterilization as described in Example 1. The resultsare included in Tables 11 and 12, with a "+" sign indicating bacterialgrowth.

                  TABLE 11                                                        ______________________________________                                        Self-Sterilizing Containers Without Breathable Window                         Temperature Packaging Type 2 hr.  6 hr.                                       ______________________________________                                        23° C.                                                                             Unpackaged tablet                                                                            +      -                                                       C/C* packaged tablet                                                                         +      -                                                       C/C packaged powder                                                                          +      -                                           40° C.                                                                             Unpackaged tablet                                                                            -      -                                                       C/C packaged tablet                                                                          -      -                                                       C/C packaged powder                                                                          -      -                                           60° C.                                                                             Unpackaged tablet                                                                            -      -                                                       C/C packaged tablet                                                                          -      -                                                       C/C packaged powder                                                                          -      -                                           ______________________________________                                         *pouch formed from CSR wrap                                              

                  TABLE 12                                                        ______________________________________                                        Self-Sterilizing Containers With Breathable CSR Window                                              0.5   1.0  1.5 2.0  3.0 4.0                             Temperature                                                                           Packaging Type                                                                              hr.   hr.  hr. hr.  hr. hr.                             ______________________________________                                        23° C.                                                                         Unpackaged tablet   +    +   +    -   -                                       Unpackaged powder   +    +   +    -   -                                       T/T* packaged tablet                                                                              +    +   +    +   -                                       T/T packaged powder +    +   +    -   -                                       C/C** packaged tablet                                                                             +    +   +    -   -                                       C/C packaged powder +    +   +    -   -                               40° C.                                                                         Unpackaged tablet                                                                           -     -    -   -                                                Unpackaged powder                                                                           -     -    -   -                                                T/T packaged tablet                                                                         +     -    -   -                                                T/T packaged powder                                                                         -     -    -   -                                                C/C packaged tablet                                                                         -     -    -   -                                                C/C packaged powder                                                                         -     -    -   -                                        60° C.                                                                         Unpackaged tablet                                                                           -     -    -   -                                                Unpackaged powder                                                                           -     -    -   -                                                T/T packaged tablet                                                                         -     -    -   -                                                T/T packaged powder                                                                         -     -    -   -                                                C/C packaged tablet                                                                         -     -    -   -                                                C/C packaged powder                                                                         -     -    -   -                                        ______________________________________                                         *- pouch formed from TYVEK                                                    ** pouch formed from CSR wrap                                            

Results from this testing show that the non-aqueous urea peroxidecomplex included in a container with and without a breathable barrierprovides effective sterilization at room temperature after only 3-4hours. At higher temperatures, sterilization is effected after as littleas one half hour.

The non-aqueous peroxide complexes which release peroxide vapor havebeen found to be useful in the sterilization of articles at roomtemperature, and more effectively, at higher temperatures. Thesecomplexes can be placed in a pouch, container, chamber, room or any areacapable of being sealed, where they release peroxide vapor whicheffectively sterilizes the articles. The complexes can be heated tofacilitate the release of vapor, and to provide sterilization in lesstime than that required for room temperature sterilization. Thecompounds of the present invention are therefore useful in a variety ofapplications where sterilization is desired. Simply by placing thecomplex in a sealed area containing an article or articles to besterilized, sterilization can be achieved. By contrast with prior artmethods, there is no need for contact with moisture to provideactivation of the hydrogen peroxide.

To confirm that sterilization can be effected using non-aqueous peroxidecomplexes in less time at lower pressures, the following experiment wasperformed.

EXAMPLE 11

A self-sterilizing container was assembled as follows: A stainless steelsupport having 9.2×10⁵ B. subtilis var. niger spores on its surface wasplaced inside a small PE vial having 20 holes (3/16" in size) in itssurface. The vial was placed in a larger PE vial, which was covered witha gas permeable layer of CSR wrap (SPUNGUARD™). Also included in thelarger vial was a second PE vial, also having 20 holes (3/16" in size)in its surface. This vial contained 1 gm urea peroxide in either powderor tablet form. The vial was then sealed in a CSR wrap or TYVEK™ pouch.

The large vials were placed in either a 4.5 L sterilization chamber or a173 L sterilization chamber. Each container was exposed to 100 torrpressure and 23° C. temperature for 2 hours, as shown in Table 13. Thebiological test samples were evaluated for sterilization as described inExample 1. The results are included in Table 13.

                  TABLE 13                                                        ______________________________________                                        Self-Sterilizing Contained With Breathable Window                             In Reduced Pressure Conditions                                                Temperature                                                                           Packaging Type 4.5 L chamber                                                                            173 L chamber                               ______________________________________                                        23° C.                                                                         Unpackaged powder                                                                            -          -                                                   T/T packaged powder                                                                          -          -                                                   C/C packaged powder                                                                          -          -                                           ______________________________________                                    

These results show that non-aqueous urea peroxide complex included in acontainer with a breathable barrier provides effective sterilization at100 torr and room temperature after only 2 hours. These results, whencompared with the results in Table 12, demonstrate that the peroxidecomplexes of the present invention provide sterilization at reducedpressures in less time than that required to effect sterilization atatmospheric pressure.

Thus, the hydrogen peroxide complexes of the present invention canprovide effective sterilization in significantly shorter periods oftime. In addition, as discussed above, plasma can also be used toenhance the sterilization activity of the hydrogen peroxide vapor. Thearticles to be sterilized are subjected to a plasma after exposure tothe peroxide vapor, and remain in the plasma for a period of timesufficient to effect complete sterilization.

Articles that have been sterilized by exposure to hydrogen peroxidevapor can be exposed to a plasma to remove any residual hydrogenperoxide remaining on the articles. Because the residual hydrogenperoxide is decomposed into non-toxic products during the plasmatreatment, the sterilized articles are ready for use followingtreatment, without the need for any additional steps.

Non-aqueous peroxide complexes are useful in a variety of applications,including as a component of self-sterilizing packaging. In addition, thecomplexes are suitable for use in various methods for vaporsterilization of articles, such as the method disclosed in U.S. Pat. No.4,943,414. This patent discloses a process in which a vessel containinga small amount of a vaporizable liquid sterilant solution is attached toa lumen, and the sterilant vaporizes and flows directly into the lumenof the article as the pressure is reduced during the sterilizationcycle. The method disclosed in the patent can be modified to allow foruse of a non-aqueous peroxide compound. The compound is placed in avessel and connected to the lumen of the article to be sterilized. Thearticle is then placed within a container and the container evacuated.The lumen of the article and the exterior of the article are contactedby the hydrogen peroxide vapor released from the non-aqueous compound. Aplasma can optionally be generated and used to enhance sterilizationand/or to remove any residual hydrogen peroxide form the article.

Use of non-aqueous peroxide complexes in the system just describedovercomes the disadvantage that the water in the aqueous solution isvaporized faster and precedes the hydrogen peroxide vapor into thelumen. Thus, more effective sterilization is achieved and less time isrequired to effect sterilization. Hydrogen peroxide complexes such asglycine anhydride are especially advantageous since they release asignificant amount of hydrogen peroxide at reduced pressure without theneed for additional heating of the complex.

Synthesis of Non-Aqueous Hydrogen Peroxide Complexes

The present invention further provides a process for preparingnon-aqueous hydrogen peroxide complexes that are useful as the source ina hydrogen peroxide vapor sterilizer, or as a component ofself-sterilizing packaging, as was described above. Of course, thehydrogen peroxide complexes can be used for other applications, such asfor bleaching agents, contact lens solutions, catalysts, and otherapplications which will be well known by those having ordinary skill inthe art.

The general procedure for preparing the hydrogen peroxide complexes ofthis invention is as follows:

(1) Place the reactant material in the chamber.

The material to be reacted with the hydrogen peroxide can be a solid invarious forms, (e.g., powder, crystal, film etc., preferably having highsurface area to increase the reaction rate). The reactant material canalso be present as a solution in water or another solvent, if sufficienttime is allowed to evaporate the solvent after the pressure is reducedin the chamber. The material may also be a liquid whose boiling point ishigher than that of hydrogen peroxide (150° C.). Since reaction ratesare faster at elevated temperature, the chamber is preferably heatedwhether before or after the reactant composition is introduced. However,the temperature should not be so high that the reactant boils orvaporizes.

The reactant composition may be contained in any container that providesaccess to the peroxide vapor. If it is in the form of a powder or otherform that may be blown about when the chamber is evacuated, then thereactant may be retained in a permeable container, which allows hydrogenperoxide to diffuse into the container.

(2) Evacuate the chamber.

Preferably, the chamber is evacuated to a pressure that is below thevapor pressure of the hydrogen peroxide (which depends on itsconcentration and temperature), in order to assure that all of theperoxide is in the vapor phase. The vapor pressure increases withincreasing temperature and decreases with increasing peroxideconcentration. For most of the experiments, the chamber was evacuated toabout 0.2 Torr and the temperature was ambient or above.

(3) Generate hydrogen peroxide vapor.

The hydrogen peroxide vapor can be generated from a hydrogen peroxidesolution or from a substantially anhydrous hydrogen peroxide complex.The latter yields dry hydrogen peroxide in the vapor state, which is anadvantage if either the material to be reacted with the vapor or thecomplex to be formed is hygroscopic. Another advantage of generating thehydrogen peroxide vapor from a substantially water-free complex is thatthe percent of hydrogen peroxide in the complex being formed is higherthan if the vapor is generated from an aqueous solution of H₂ O₂. Thisis probably due to the competition between water molecules and H₂ O₂molecules for bonding sites on the complex when an aqueous solution isused to generate the H₂ O₂ vapor.

The peroxide vapor can be generated within the same chamber that housesthe reactant material or in another chamber separated from it by avacuum valve.

(4) React the reactant material with hydrogen peroxide.

The time required for the reaction depends, of course, on the reactionrate of the reactant with hydrogen peroxide. It can be empiricallydetermined by monitoring the pressure, which decreases during thebinding of peroxide to the reactant material. Typically, the reactiontime is about 5-30 minutes. The concentration of vaporized hydrogenperoxide and the weight of the starting material determine the weightpercentage of peroxide in the final reaction product. As the weightratio of reactant to hydrogen peroxide increases, the weight percentageof hydrogen peroxide in the complex decreases. The reaction can berepeated multiple times to increase the concentration of hydrogenperoxide in the complex.

(5) Evacuate the chamber again.

At the end of the reaction period, the chamber is further evacuated toabout 2 Torr to remove any unreacted hydrogen peroxide.

(6) Vent the chamber and retrieve the hydrogen peroxide complex.

The mechanism by which the hydrogen peroxide forms a complex with thereactant material is not completely understood. The formation of thecomplex is believed to involve hydrogen bond formation between thehydrogen peroxide and electron-rich functional groups containing oxygenand/or nitrogen on the reactant material. It is not known if this is theonly mode of binding; however, materials with a wide range of functionalgroups have been found to form complexes with hydrogen peroxide.

The advantages of the vapor phase reaction over earlier methods ofhydrogen peroxide complex formation include:

1. The ratio of hydrogen peroxide to reactant material can be accuratelycontrolled by varying the amount of hydrogen peroxide present in thevapor state or the amount of reactant material exposed to the vapor.

2. The need to remove solvent from the reaction product is eliminated.

3. Peroxide complexes can be formed that are liquid or solids, such aspowders, crystals, films, etc.

4. Peroxide complexes of hygroscopic materials can be prepared.

The synthesis of the non-aqueous peroxide complexes according to thepresent invention is further described in the following examples. Manyof these compounds have utility as catalysts, in addition to having theutilities described in greater detail herein, as will be readilyappreciated by those having ordinary skill in the art. The examplesrepresent embodiments of the compositions and processes of theinvention, but they are not in any way intended to limit the scope ofthe invention,

EXAMPLE 12

A hydrogen peroxide complex of glycine anhydride was prepared asfollows: A 1.0 gram sample of glycine anhydride (Aldrich Chemical Co.,Milwaukee, Wis.) was placed in an aluminum tray in a 173 liter chambermaintained at a temperature of 45° C. The top of the aluminum tray wascovered with TYVEK™ nonwoven fabric, which prevented the glycineanhydride from coming out of the tray when the pressure in the chamberwas reduced but was breathable and did not absorb hydrogen peroxide. Thechamber door was closed and the pressure in the chamber was reduced to0.2 Torr by evacuating the chamber with a vacuum pump. A hydrogenperoxide concentration of 10 mg/liter was created by evaporation of anappropriate volume of a 70% aqueous solution of hydrogen peroxide (FMCCorp., Philadelphia, Pa.) into the chamber. The hydrogen peroxide vaporwas maintained in contact with the glycine anhydride for 20 minutes. Atthe end of the reaction period, the chamber pressure was reduced to 2Torr and then returned to atmospheric pressure. The reaction product wasremoved from the chamber and analyzed for weight percent hydrogenperoxide by the following iodometric titration reactions.

    H.sub.2 O.sub.2 +2KI+H.sub.2 SO.sub.4 →I.sub.2 +K.sub.2 SO.sub.4 +2H.sub.2 O

    I.sub.2 +2Na.sub.2 S.sub.2 O.sub.3 →Na.sub.2 S.sub.4 O.sub.6 +2Nal

A starch indicator was used in the iodine-sodium thiosulfate titrationreaction to enhance the color change at the end point. The percentage byweight of hydrogen peroxide was calculated by the following equation:

    wt % H.sub.2 O.sub.2 =[(ml of Na.sub.2 S.sub.2 O.sub.3)*(normality of Na.sub.2 S.sub.2 O.sub.3)*1.7]/(sample weight in grams)

The weight percentage of hydrogen peroxide in the glycine anhydridecomplex was found to be 24.3%.

EXAMPLE 13

The hydrogen peroxide complexes of a wide variety of organic andinorganic complexes were prepared using the procedure of Example 12. Ineach case, the reaction conditions were the same as those in Example 12,except 1.0 gram of each one of the compounds presented in Table 14 wasused in place of glycine anhydride.

                                      TABLE 14                                    __________________________________________________________________________    COMPOUNDS EVALUATED AND WEIGHT PERCENT HYDROGEN PEROXIDE                      PRESENT IN COMPLEXES FORMED BY VAPOR PHASE SYNTHESIS PROCESS                                                 Wt % After                                                                    Peroxide                                       Chemical Name                                                                              Chemical Structure                                                                              Treatment                                                                           Category                                 __________________________________________________________________________    Poly(vinyl alcohol)                                                                        [CH.sub.2 CH(OH)].sub.n                                                                         18.9% Alcohol                                  Poly(vinyl methyl ether)                                                                   [CH.sub.2 CH(OCH.sub.3)].sub.n                                                                  22.0% Ether                                    Poly(vinyl methyl Ketone)                                                                  [CH.sub.2 CH(COCH.sub.3)].sub.n                                                                 13.9% Ketone                                   Poly(acrylic acid)                                                                         [CH.sub.2 CH(COOH)].sub.n                                                                        5.1% Acid                                     Glycine      H.sub.2 C(NH.sub.2)(COOH)                                                                       20.7% Amino Acid                               L-Histidine                                                                                 ##STR1##         14.1% Amino Acid                               Poly(vinyl acetate)                                                                        [CH.sub.2 CH(OCOCH.sub.3)].sub.n                                                                 9.1% Ester                                    Cellulose acetate              10.9% Ester                                    Sodium alginate                27.7% Organic Salt                             Cellulose sulfate, sodium salt 18.2% Organic Salt                             Poly(4-Vinylpyridine)                                                                      [CH.sub.2 CH(ρ-C.sub.5 H.sub.4 N)].sub.n                                                    21.8% Aromatic amine                           Histamine                                                                                   ##STR2##         13.2% Amine                                    Propionamide (C.sub.2 H.sub.5)CONH.sub.2                                                                     31.8% Amide                                    Urea         (H.sub.2 N).sub.2 CO                                                                            17.9% Urea                                     1,3-dimethylurea                                                                           (H.sub.3 C)HNCONH(CH.sub.3)                                                                     31.7% Urea                                     Biuret       (H.sub.2 N)CO(NH)CO(NH.sub.2)                                                                   13.7% Biuret                                   Polyacrylamide                                                                             [CH.sub.2 CH(CONH.sub.2)].sub.n                                                                 30.1% Polyamide                                Polyvinylpyrrolidone                                                                        ##STR3##         29.9% Polyamide                                Nylon 6      [NH(CH.sub.2).sub.5 CO].sub.n                                                                   17.1% Polyamide                                Nylon 6,6 film                                                                             [NH(CH.sub.2).sub.6 NHCO(CH.sub.2).sub.4 CO].sub.n                                              16.6% Polyamide                                Polyetherpolyurethane                                                                      [RHNCOOR'].sub.n   9.5% Polyurethane                             Sodium carbonate                                                                           Na.sub.2 CO.sub.3 14.3% Inorganic                                Potassium carbonate                                                                        K.sub.2 CO.sub.3  33.9% Inorganic                                Rubidium carbonate                                                                         Rb.sub.2 CO.sub.3 37.0% Inorganic                                Calcium hydroxide                                                                          Ca(OH).sub.2      23.4% Inorganic                                Sodium bicarbonate                                                                         NaHCO.sub.3       10.7% Inorganic                                Tetrasodium pyrophosphate                                                                  Na.sub.4 P.sub.2 O.sub.7                                                                        18.9% Inorganic                                __________________________________________________________________________

The organic complexes formed cover the following range of functionalgroups that are capable of forming hydrogen bonds with hydrogenperoxide: alcohols, ethers, ketones, acids, amino acids, esters, organicsalts, amines, amides, polyamides, polyurethanes, ureas, and biuret. Theinorganic complexes include carbonates with sodium, potassium, andrubidium cations, as well as sodium bicarbonate. In addition, thehydrogen peroxide complexes of calcium hydroxide and tetrasodiumpyrophosphate were also prepared. The starting materials were finelydivided powers or slightly larger crystalline materials, except fornylon 6,6, which was processed as a film with a thickness of 0.12 mm,and polyvinyl methyl ether, which was a 50% by weight aqueous solution.

The hydrogen peroxide complexes obtained with these materials under thetest conditions were solids, except for polyvinylpyrrolidone, histamine,poly(vinyl methyl ether), poly(vinyl methyl ketone),propionamide, and1,3-dimethylurea. The 1,3-dimethylurea and propionamide hydrogenperoxide complexes were free flowing liquids that were easily handled inthe vapor phase synthesis process, since no solvent needed to be removedto obtain the final product. The histamine, polyvinylpyrrolidone,poly(vinyl methyl ether), and poly(vinyl methyl ketone) complexes weregummy materials that were not as easy to handle.

Example 14 and 15 describe additional studies with polyvinylpyrrolidoneunder different process conditions to obtain the peroxide complex as afree flowing solid product.

EXAMPLE 14

Hydrogen peroxide complexes with polyvinylpyrrolidone were prepared inwhich the percent hydrogen peroxide in the polyvinylpyrrolidone complexwas varied by changing the ratio of the weight of polyvinylpyrrolidoneto the concentration of hydrogen peroxide in the vapor state. Theconditions in these tests were identical to those in Example 12, exceptthe weight of polyvinylpyrrolidone was increased from 1.0 gram to 3.0grams to 5.0 grams. In all tests, the concentration of hydrogen peroxidewas held constant at 10.0 mg/liter of chamber volume. The results ofthese tests are presented in Table 15.

EXAMPLE 15

A hydrogen peroxide complex of PVP was prepared in which the hydrogenperoxide was delivered from a complex of hydrogen peroxide with urea.When hydrogen peroxide is delivered in this manner, it is substantiallywater free. In this test, 5 grams of PVP was placed in the reactionchamber and 10 mg H₂ O₂ /liter of chamber volume was delivered into thereaction chamber by heating about 7 grams of a 35% complex of H₂ O₂ withurea to a temperature of about 110° C. for approximately 5 minutes. Therest of the conditions in this test were the same as those in Example12. The percentage hydrogen peroxide in the PVP complex and the physicalstate of the complex are presented in Table 15.

                  TABLE 15                                                        ______________________________________                                        EFFECT OF RATIO OF POLYVINYLPYRROLIDONE TO                                    HYDROGEN PEROXIDE IN THE VAPOR STATE ON % HYDROGEN                            PEROXIDE IN COMPLEX AND PHYSICAL STATE OF PRODUCT                                    Weight                                                                              Wt % H.sub.2 O.sub.2                                                                      Physical State                                              PVP (g)                                                                             in Complex  of Product                                           ______________________________________                                        Ex. 14   1       29.9        Soft gummy product                                        3       23.5        Hard gummy product                                        5       17.7        Free flowing solid                               Ex. 15   5       19.7        Free flowing solid                               ______________________________________                                    

The results of these tests demonstrate that a free flowing solid can beobtained with the PVP hydrogen peroxide complex by controlling the ratioof PVP to hydrogen peroxide in the vapor state and, alternatively, byusing a substantially water-free hydrogen peroxide vapor source.

INORGANIC HYDROGEN PEROXIDE COMPLEXES

Inorganic hydrogen peroxide complexes are also suitable for use assterilants as described in detail hereinabove for organic hydrogenperoxide complexes. Peroxide vapor can be released from these inorganiccomplexes at atmospheric pressure and room temperature. However, asdescribed in greater detail below, substantial amounts of hydrogenperoxide vapor can be released from inorganic peroxide complexes uponrapid heating to a particular release temperature under reducedpressure. In order to successfully release hydrogen peroxide frominorganic peroxide, the heating rate of the inorganic peroxide complexesis preferably at least 5° C./min; more preferably it is at least 10° C.per minute; still more preferably at least 50° C./min.; and mostpreferably, it is at least 1000° C. per minute.

A representative listing of these inorganic peroxide complexes, and theweight percent hydrogen peroxide, is presented in Table 16. Thetitration procedure used to determine the weight percent of H₂ O₂ in thecomplexes was as described in Example 12. Sodium carbonate H₂ O₂ complexwas purchased from Fluka Chemical Corp. The vapor-phase synthesisprocedure used for synthesizing the inorganic peroxide complexes was thesame as that disclosed in Example 12, with the exceptions that 10 g ofthe solid inorganic sample instead of 1-5 g, and two reaction cyclesversus one, were employed.

EXAMPLE 16

The reaction procedure for liquid-phase synthesis of inorganic hydrogenperoxide complexes was essentially as described by Jones et al. (J.Chem. Soc., Dalton, 12:2526-2532, 1980). Briefly, inorganic solids werefirst dissolved in a 30% aqueous solution of hydrogen peroxide to make asaturated solution, followed by dropwise addition of ethanol. For thepotassium oxalate and rubidium carbonate complexes, the white peroxideprecipitates were formed as the amount of ethanol added was graduallyincreased. For potassium carbonate, potassium pyrophosphate and sodiumpyrophosphate, the saturated solutions were incubated at -10° C. forseveral hours to facilitate crystalline peroxide complex formation. Thecomplexes were separated from the liquid by vacuum filtration, washedwith ethanol at least three times and dried by vacuum.

                  TABLE 16                                                        ______________________________________                                        COMPOUNDS EVALUATED AND WEIGHT PERCENT HYDROGEN                               PEROXIDE PRESENT IN COMPLEXES                                                                        Wt % H.sub.2 O.sub.2                                   Chemical      Chemical in Complexes.sup.1                                     Name          Formula  Purchased.sup.2                                                                         Vapor.sup.3                                                                         Liquid.sup.3                           ______________________________________                                        Sodium Carbonate                                                                            Na.sub.2 CO.sub.3                                                                      27.35                                                  Potassium Carbonate                                                                         K.sub.2 CO.sub.3   7.43  22.70                                  Robidium Carbonate                                                                          Rb.sub.2 CO.sub.3  20.31 26.78                                  Potassium Oxalate                                                                           K.sub.2 C.sub.2 O.sub.4                                                                          16.13 16.42                                  Sodium Pyrophosphate                                                                        Na.sub.4 P.sub.2 O.sub.7                                                                         11.48 23.49                                  Potassium Pyrophosphate                                                                     K.sub.4 P.sub.2 O.sub.7                                                                          20.90 32.76                                  Sodium Orthophosphate                                                                       Na.sub.3 PO.sub.4  15.67                                        Potassium Orthophosphate                                                                    K.sub.3 PO.sub.4   16.11                                        ______________________________________                                         .sup.1 The titration procedure employed to determine the weight percent o     H.sub.2 O.sub.2 in the complexes is the same as the one stated in the         previous patent application.                                                  .sup.2 Sodium carbonate hydrogen peroxide complex was purchased from Fluk     Chemical Corp.                                                                .sup.3 The vapor and liquid phase procedures were used for synthesizing       the inorganic peroxide.                                                  

A differential scanning calorimeter (DSC) (Model PDSC 2920, TAinstruments) was used to determine H₂ O₂ release or decompositionproperties of the inorganic peroxide complexes. The DSC was run at aheating ramp of 10° C./min and at a temperature range of between 30° C.and 200° C. under both atmospheric and varying vacuum pressureconditions. Referring now to FIG. 5, the DSC comprises a sample chamber110, heating plate 112 and pressure control system. The pressure controlsystem comprises a pressure transducer 114 connected to a pressure gauge116. The pressure gauge 116 is connected to a controller 118 which is,in turn, connected to a pressure control valve 120. The pressuretransducer 114 is in fluid communication with pressure control valve 120and with pump 122.

Potassium oxalate hydrogen peroxide complex synthesized as describedhereinabove was placed in a DSC and subjected to a particular vacuumpressure over a temperature range of 50° C. to 170° C. As can be seen inFIG. 6, greater release of H₂ O₂, an endothermic process, occurred atlower pressures, while the exothermic decomposition of H₂ O₂ was favoredat higher pressures. The partial vacuum pressure is preferably less than20 torr and most preferably less than 10 torr. The actual pressure inthe sample chamber is somewhat higher than that measured within theapparatus and the actual temperature of the chamber is somewhat lowerthan that measured of the metal plate or aluminum platen. Withoutwishing to be bound by any particular theory of operation, it isbelieved that the actual pressure used in the sterilization apparatusshould be less than the vapor pressure of the inorganic peroxide complexat the actual temperature of the chamber in order to ensure that thecomplex will release hydrogen peroxide vapor with substantially nodecomposition. However, in general, the pressure used is preferably lessthan 50 torr, more preferably less than 10 torr. In certain embodimentsof the invention in which the vapor pressure of the peroxide complex islow, the pressure is preferably less than 5 torr.

In the use of the inorganic peroxide complexes for sterilization, it iscritical to complex stability that heating occur rapidly which may beeffected by preheating the aluminum plate prior to contacting with theinorganic peroxide composition. In the use of the inorganic peroxidecompounds, it is also preferred that the temperature be higher than 86°C.

As discussed above, it is preferred that the inorganic hydrogen peroxidecomplex be heated rapidly, i.e. as rapidly as 1000° C./minute or more.This can be accomplished by contacting the peroxide with a pre-heatedheating plate. A preferred embodiment for accomplishing such rapidheating is shown in FIGS. 7A and 7B. Referring to FIG. 7A, there isshown an apparatus 125 for injecting peroxide vapor into a sterilizationchamber 131 in a closed position. The inorganic hydrogen peroxidecomplex is incorporated into a peroxide disk 132. The disk 132 comprisesfive layers: three layers of CSR wrap, peroxide complex powder andaluminum foil coated with polypropylene. The disk 132 is heat sealedaround its edge to retain the peroxide complex powder. The peroxide disk132 is placed underneath a perforated aluminum plate 130 which isattached to housing 150 by aluminum attachment pieces 142. The disk 132is loosely held in place between O-rings 151. Prior to introduction ofperoxide vapor into the chamber, a heated aluminum platen 134 is apartfrom the peroxide disk 132 and is attached to an aluminum plate 136. Aspring (not shown) within the bellow 138 holds the plate 136 down in theclosed position. When the chamber 131 is evacuated, the bellow 138 isalso evacuated. The plate 136 is seated against O-rings 148, thusseparating a peroxide release chamber 152 from passageways 158. Theapparatus is held in place and attached to a sterilization chamber 131by bolts 144, 146, 154 and 156.

Referring to FIG. 7B, in order to bring the platen 134 up to contact theperoxide disk 132, the bellow 138 is vented. Once the pressure isincreased, the bellow 138 moves upward, thereby propeling the heatedaluminum platen 134 against the peroxide disk 132. In a preferredembodiment, the aluminum platen 134 is pre-heated to 175° C.; howeverother temperatures can be used. Peroxide vapor is then released from thepowder through the CSP layers, passes through the perforations 160 inthe perforated aluminum plate 130, and enters the peroxide releasechamber 152. The upward movement of the heated aluminum platen 134 alsoopens the peroxide release chamber 152, allowing peroxide vapor to enterpassageways 158 which are in fluid communication with the sterilizationchamber.

The inorganic peroxide complexes used in the following two examples todetermine amount of peroxide release and sterilization efficacy werepotassium pyrophosphate (K₄ P₂ O₇.3H₂ O₂ :PP), potassium oxalate (K₂ C₂O₄.1H₂ O₂ :PO) and sodium carbonate (Na₂ CO₃.1.5H₂ O₂ :SC).

EXAMPLE 17 Release of Peroxide from SC, PO and PP

The ideal temperature at which H₂ O₂ was released from SC, PO and PP wasdetermined by DSC. The actual amount of H₂ O₂ released from 2 g of eachof these complexes was determined at various temperatures using a 75liter chamber and the apparatus of FIGS. 7A and 7B. The amount of H₂ O₂released from the PP at 175° C. was greater than for SC and PO. AlthoughSC released the least amount of H₂ O₂ at 175° C., significantly morerelease was seen when the amount of sample was increased.

                  TABLE 17                                                        ______________________________________                                        RELEASE OF PEROXIDE IN 75 LITER CHAMBER                                                    SC      PO        PP                                             ______________________________________                                        Temp. to release H.sub.2 O.sub.2                                                             170° C.                                                                          150° C.                                                                          130° C.                             (by DSC)                                                                      With 2 grams sample                                                           At 125° C.                                                                            0.3 mg/L  0.8 mg/L  1.0 mg/L                                   At 150° C.                                                                            1.2 mg/L  2.0 mg/L  1.5 mg/L                                   At 175° C.                                                                            1.8 mg/L  2.5 mg/L  3.4 mg/L                                   With 3 grams sample                                                                          2.3 mg/L                                                       At 175° C.                                                             With 4 grams sample                                                                          2.9 mg/L                                                       At 175° C.                                                             ______________________________________                                    

EXAMPLE 18 Efficacy tests using SC, PO and PP

2×10⁶ B. subtilis var. niger spores were inoculated on a SS blade. Threeinoculated blades were first placed in the front, middle and backpositions of a Spunguard wrapped 10"×21"×3.5" polyphenylene oxide tray.The wrapped tray was then placed in a 75 liter vacuum chamber having aninitial vacuum pressure of 0.2 torr. A 5.5" peroxide disk was made byheatsealing the SC, SO or PP inorganic peroxide powders between threelayers of Spunguard and one layer of aluminum foil coated withpolypropylene film. The peroxide was released by contacting the disk for2 minutes with an aluminum plate which had been preheated to 175° C.,followed by an additional diffusion time of 8 minutes for a totalexposure time of 10 minutes. After treatment, the three blades wereseparately placed in Trypticase Soy Broth (TSB) at 32° C. for 7 days andscored for bacterial growth. The results are summarized in Table 18.

                  TABLE 18                                                        ______________________________________                                        EFFICACY TEST RESULTS                                                         Peroxide  Weight of    Peroxide Sterility                                     Complex   Complex      Conc.    (+/all)                                       ______________________________________                                        PP        2 grams      3.4 mg/l 0/3                                           PO        2 grams      2.5 mg/l 0/3                                           SC        2 grams      1.8 mg/l 1/3                                           SC        3 grams      2.3 mg/l 0/3                                           SC        4 grams      2.9 mg/l 0/3                                           ______________________________________                                    

As can be seen in the table, no growth of spores was observed with theexception of 2 g SC (1/3). However, when the amount of SC subjected tovaporization was increased to 3 grams, no bacterial growth was observed.These results underscore the efficacy of sterilization using inorganichydrogen peroxide compound.

Inorganic hydrogen peroxide complexes can be readily incorporated intothe sterilization procedures described hereinabove in connection withorganic peroxide complexes. For example, inorganic complexes can be usedin connection with a plasma sterilization method, or in connection witha self-sterilizing enclosure where peroxide is slowly released from thecomplex. Similarly, inorganic complexes can also be used in thesterilization of articles having narrow lumens, whereby a vesselcontaining the inorganic peroxide complex is connected to the lumen. Inaddition, pressure pulsing of the vapor released from inorganic peroxidecomplexes can be employed. Other examples of the use of inorganiccomplexes for sterilization will be apparent to one having ordinaryskill in the art upon reference to the present specification.

We claim:
 1. An apparatus for hydrogen peroxide sterilization of anarticle, comprising:a container for holding the article to be sterilizedat a pressure of less than 50 torr; and a source of hydrogen peroxidevapor in fluid communication with said container, said source comprisinga non-aqueous inorganic hydrogen peroxide complex which does notdecompose to release a hydrohalic acid, said complex being at atemperature greater than 86° C., said source configured so that saidvapor can contact said article to effect sterilization.
 2. The apparatusof claim 1, wherein said pressure is less than 20 torr.
 3. The apparatusof claim 1, wherein said pressure is less than 10 torr.
 4. The apparatusof claim 1, wherein said source is located within said container.
 5. Theapparatus of claim 1, further comprising an enclosure disposed outsideof said container in which said complex is located, and an inletproviding fluid communication between said container and said enclosure,such that vapor released from said complex travels along said inlet andinto said container to effect sterilization.
 6. The apparatus of claim1, wherein said inorganic hydrogen peroxide complex is a complex ofsodium carbonate, potassium pyrophosphate or potassium oxalate.
 7. Theapparatus of claim 1, further comprising a heater located within saidcontainer, whereby said complex is placed on said heater and heated tofacilitate the release of said vapor from said complex.
 8. The apparatusof claim 7, wherein said heater is heated prior to contacting with saidcomplex.
 9. The apparatus of claim 1, further comprising a vacuum pumpin fluid communication with said container for evacuating the container.10. The apparatus of claim 1, further comprising an electrodeconstructed and arranged to generate a plasma around said article. 11.The apparatus of claim 10, wherein said electrode is inside saidcontainer.
 12. The apparatus of claim 10, wherein said electrode isspaced apart from said container and is constructed and arranged to flowplasma generated thereby towards and around said article.
 13. Theapparatus of claim 1, wherein said complex is in a solid phase.
 14. Amethod for hydrogen peroxide vapor sterilization of an article,comprising:placing said article into a container; and inorganic hydrogenperoxide complex which does not decompose to release a hydrohalic acidby heating the complex at a rate of at least 5° C./minute to contact andsterilize the article.
 15. The method of claim 14, wherein the heatingrate is at least 10° C./minute.
 16. The method of claim 14, wherein theheating rate is at least 50° C./minute.
 17. The method of claim 14,wherein the heating rate is at least 1000° C./minute.
 18. The method ofclaim 14, wherein the complex has less than 10% water.
 19. The method ofclaim 14, wherein the heating step comprises contacting said complexwith a pre-heated heater.
 20. The method of claim 14, wherein saidcomplex is heated to a temperature greater than 86° C.
 21. The method ofclaim 14, further comprising evacuating the container before introducingsaid vapor into said container at a pressure of less than 50 torr. 22.The method of claim 21, wherein said pressure is less than 20 torr. 23.The method of claim 21, wherein said pressure is less than 10 torr. 24.The method of claim 14, further comprising generating a plasma aroundsaid article after introducing, said vapor into said container.
 25. Themethod of claim 24, wherein said plasma is generated inside thecontainer.
 26. The method of claim 24, wherein said plasma is generatedoutside the container and flowed inside the container and around saidarticle.
 27. The method of claim 14, wherein the contacting stepcomprises pressure pulsing of said vapor.
 28. A method for hydrogenperoxide sterilization of an article, comprising:placing the article ina enclosure containing an inorganic hydrogen peroxide complex; sealingsaid enclosure; and allowing said enclosure to stand at a temperaturebelow 70° C. for a time sufficient to release hydrogen peroxide vaporfrom said complex to effect sterilization of the article.
 29. The methodof claim 28, wherein said enclosure is allowed to stand at a pressureless than atmospheric pressure.
 30. The method of claim 28, wherein saidenclosure is allowed to stand at a temperature below about 40° C. 31.The method of claim 28, wherein said enclosure is heated to atemperature greater than 23° C. to facilitate release of said vapor. 32.The method of claim 28, wherein said enclosure is selected from thegroup consisting of a pouch, a container, a chamber and a room.
 33. Themethod of claim 28, wherein said hydrogen peroxide complex is in theform of a powder.
 34. The method of claim 28, wherein said hydrogenperoxide complex is in the form of a tablet.
 35. The method of claim 28,wherein said sealing step comprises sealing said enclosure with a gaspermeable material.
 36. The method of claim 35, wherein said gaspermeable material is selected from the group consisting of TYVEK™, CSRwrap, and paper.
 37. A sealed enclosure containing a sterile product andan inorganic hydrogen peroxide complex capable of releasing hydrogenperoxide vapor, and which does not decompose to release a hydrohalicacid.
 38. A method for hydrogen peroxide vapor sterilization of anarticle, comprising:placing said article into a container; andcontacting the article with a hydrogen peroxide vapor to contact andsterilize the article, said vapor being released from an inorganichydrogen peroxide complex which does not decompose to release ahydrohalic acid.
 39. A method for hydrogen peroxide sterilization of anarticle having an exterior and a narrow lumen therein,comprising:connecting a vessel containing an inorganic peroxide complexwhich does not decompose to release a hydrohalic acid to the lumen ofthe article; placing the article within a container, whereby said vesselremains connected to the lumen; reducing the pressure within saidcontainer; and contacting the lumen of the article with hydrogenperoxide vapor released from said inorganic peroxide complex at atemperature less than 70° C.